1. Field of the Invention
The invention relates to a device for transplanting trees or bushes. The device contains a series of digging spades having corrugated edges.
2. Prior Art
A device for transplanting trees is known from German Patent 31 09 727 A1 that comprises two digging spades in the shape of one quarter sphere. These digging spades can be displaced and pivoted against each other, whereby they complement one another in a closed position, forming a semispherical cup. The edge surfaces of these digging spades, are directed downwards in an open starting position. These edges have a zigzag shape, so that these digging spades have a row of teeth. These teeth have ground surfaces whose outer edges are shaped into cutting blades. The cutting blades help the digging spades penetrate into the ground especially when severing the roots of the tree to be transplanted. While this device has been successfully used in practical applications, it was found that there is a need for further improvements. In particular, it was found that the teeth may break off if they are pressed against stones embedded in the soil.
A single-ball undercutting and lifting device is known from German Patent 39 43 053 A1. This device is substantially formed by two slim blades, which are pivotally-mounted, and swing about a common axle. These cutting blades have ground or finished surfaces shaped in a sinusoidal manner.
A device for digging out plants is known from German Patent 30 08 009 A1. This device has spades with cutting blades that are smooth in front. These spades can be pivoted against each other and partially overlap one another in a closed position. The smooth cutting blades are exposed to the risk of becoming blunt and getting bent by the stones embedded in the soil.
Therefore, the invention provides a device capable of cutting through the roots when a tree or shrub is lifted out, while the design of this device requires fewer repairs.
The device of the invention has two spades that can be adjusted against each other for digging and transplanting trees or bushes. These open spades are spaced apart from each other by at least the diameter of a tree trunk. Thus these spades can be moved past the trunk of the tree into a position where they embrace the tree or bush to be transplanted. The spades have cutting blades that are directed downwards when opened. Furthermore, these spades are actively connected with a servo-drive, or hydraulic drive, which adjusts and swivels the spades in relation to each other.
In this adjustment process, the spades are first set so that the cutting blades complement each other to form a substantially circular shape embracing the tree or bush to be transplanted on all sides.
The spades are pivoted in relation to each other about an axis approximately extending through a common center point, so that they penetrate the soil surrounding the tree to be transplanted. Two or more spades can be used, however, the individual spades should substantially complement each other in a closed position to form a semi-spherical cup. Because of the special form of the spades, their surfaces always extend in the zone of the cut produced by the cutting blades. This design assures that the spades can be driven through the soil with relatively little use of force.
However, often when trees or bushes are transplanted, the spades are pressed against rocks embedded in the soil. To reduce the damage to the spades caused by rocks, the cutting blades have edges that are ground in a corrugated manner. The corrugated edges have alternating elevations and concave recesses, so that the cutting blade, as viewed in the cross section, has acute angles. With this design the cutting blade has sufficient stability when the soil is penetrated because of the elevations. These edges could also have a chamfer or rounding without impairing the function of the corrugated ground edges. These corrugated ground edges of the cutting blade are only corrugated to a minor extent.
Thus, while cutting blades are normally susceptible to fracture, the projecting sections are disposed in an area of material thickenings to reduce the rate of fracture. The cutting blade can consequently be highly stressed, while the soil nonetheless exerts only minor resistance to the blade. Therefore, this spade is far tougher than previous designs and provides an easy penetration of the soil.
In another embodiment of the invention, the spades have cutting blades disposed on either side. When only two spades are used, the cutting blade is disposed on the inside of one of the spades, and on the outside of the other spade. However, if the number of spades is increased, it is necessary to provide approximately half of these spades with cutting blades located on the inside face, and the other half with cutting blades located on the outside face. The transition between two cutting blades is disposed on the lower points of the spades. In the closed position, the ground surfaces of the cutting blades partially overlap one another so that the ground surfaces of the spades come to rest against each other. Thus the cutting blades can correctly sever the thicker roots such as the tap root of the tree to be replaced, especially when these roots are located in where the cutting blades meet in their closed position.
To further reduce the risk of breaking the cutting blade, the elevations of the corrugated, ground edging should be capped on their end sides. This will further reduce the waviness of the contour of the cutting blade, so that the protruding parts of the ground surface are formed substantially parallel with the contour of the cutting blade. The contour of the cutting blade has no projecting corners exposed to any increased risk of fracture. The blade contour, formed by the counter edges, is thus acutely angular as viewed in the direction of movement of the spades, so that the thicker roots can be easily severed.
Furthermore, the elevations of the cutting blades should be offset in relation to each other. In this way, the elevations of one cutting blade engage the recesses of the opposite cutting blade, so that the blades will not mutually obstruct each other. The two cutting blades can be extensively overlapped when the spades are in the closed position, so that downward extending roots of the tree can be reliably severed.
If the spacing between the elevations of the corrugated, ground edges of the cutting blades is too large in relation to the thickness of the spade, the cutting blade will no longer have the required stability within the zone of the recesses. Thus, this blade may be damaged by rocks embedded in the soil. However, if the spacing between the elevations is too small, these elevations will offer excessive resistance to the soil as the spade penetrates the soil. With a spade thickness of about 10 mm, a spacing of between 15 and 60 mm between the elevations was found to be successful, whereby a spacing of about 30 mm is preferred.
In one embodiment, the cutting blade basically could be joined with the spade as one single piece. However, in a second embodiment, the cutting blade should have a separate edge that is retained on the spade. This separate edge has a greater hardness than the spade, so that the blade has a particularly long life. This spade also has sufficient elasticity, so that it is capable of giving way to any rocks embedded in the soil, without excessively stressing the cutting blade. To fix the separate edge on the spade, the spades and the separate edge should be welded to each other. Thus, the joint between the separate edge and the spade can be highly stressed, with no fastening means projecting beyond the spade on the inner or outer sides. This protruding fastening means would have the drawback of exerting additional resistance to the spade as the spade penetrates the soil, and consequently would be subjected to increased stress as well.
The separate edge could be placed on the face of the spade in a butt-jointed manner. However, it is better if the surface of the cutting blade is tapered in the form of steps, and the end of the spade is shaped to conform to this stepped tapering. The separate edge is preferably retained on the spade by means of a tongue and groove profile capable of absorbing lateral forces. The pressure forces exerted on the separate edge are directly absorbed by the face of the spade, so that there is no need for an additional holding means. These holding means therefore could be used in a weaker form and thus in a space-saving manner, so that no components protrude beyond the spade. For example, the separate edge could be retained on the spade by spot-welded points or countersunk screws.
If the separate edge is joined with the spade by detachable holding means, the replacement of these separate edges is simplified when the cutting blade shows too much wear. Countersunk screws that do not project beyond the spade are preferably used as a holding means.
Finally, in another improvement of the invention a plurality of parts is provided with cutting blades and are retained on the spade, so that only the segment that was damaged during use need be replaced. This reduces the costs for maintaining the device.